The present invention constitutes an improvement on the end closure constructions taught in U.S. Pat. No. 3,746,244, issued July 17, 1973, entitled "Sift-Proof Carton Construction", and U.S. Pat. No. 3,981,432, issued Sept. 21, 1976, entitled "Carton With Tightly Sealed End Closures".
The first of the aforementioned patents teaches an improved sift-proof carton construction wherein a plurality of the carton end closure flaps are provided with mating sets of ridges or grooves which interengage when the flaps are juxtaposed and sealed together, thereby providing barriers acting to prevent the sifting and leakage of powdered or granular materials from between the end closure flaps. The ridges or grooves are defined in the carton flaps by scoring rules similar to those employed to define the hinge lines connecting the various wall panels and end closure flaps to each other. The scoring rules effectively emboss the boxboard, defining a groove on the side of the board contacted by the rule and a ridge on the opposite side of the board. The positioning of the ridges and grooves is such that they will mate when the flaps are closed and sealed, thereby providing barriers which effectively prevent sifting and leakage of the contents from between the flaps.
The second of the above mentioned patents teaches ways of further enhancing the sift-proof character of the end closures utilizing opposing pairs of innermost end closure flaps which are folded upon themselves to form double thickness flap members adapted to enter into wedging engagement with the score lines by means of which the flaps are hingedly connected to the carton body walls. In order to insure tight sealing at the corners of the end closures, the double thickness flap parts are provided at their innermost ends with relatively small laterally projecting ears which, when the flaps are infolded and sealed, wedge in the corners of the cartons, thereby acting to close and seal "pin-holes" or interstices which may exist at the corners of the carton.
The present invention relates to a simplified way of sealing "pin-holes" and interstices which may form at the corner edges of the carton.